The principal defect in bullous pemphigoid is the separation of the basal cell layer from the extracellular matrix portion of the BMZ. We will develop an in vitro model of epidermal cells (human keratinocytes and PAM 212) grown on EHS sarcoma matrix extract (known to contain laminin and type IV collagen) to simulate the in vivo relationship of epidermal cells and the BMZ. Others have shown that cryostat sections of skin will fix complement and mediate chemoattraction of PMN's in vitro. We will examine the ability of the basal cell/matrix model to 1) fix and activate complement from normal human serum; 2) release chemotactic complement products and produce an "activated" supernatant. Degranulation of mast cells is prominent in lesions of BP. The stimulus for release of mast cell products including histamine, ECF-A and HMW-NCF is unknown but could be complement (C3a, C5a) or lymphocyte (HRA) derived. We will investigate the mast cell with respect to 1) response to in vitro derived complement activation products; 2) lymphocyte derived HRA; 3) response to "activated" supernatant with ECF-A, HMW-NCF and histamine release; 4) direct cytotoxic effect in the epidermal/matrix model. Eosinophils and PMN's are felt to be attracted to the BMZ by complement or mast cell derived chemoattractants and perhaps to be essential in the full development of dermal epidermal separation. The cells will be evaluated for 1) response to "activated" supernatant in chemotaxis experiments; 2) the ability to bind to antibody-complement complexes on cell/matrix cultures; 3) ability to mediate direct cell lysis in culture. The lymphocyte, also present in inflammatory infiltrates, may play a role by release of mast cell products via HRA or by direct cytotoxic effect on epidermal cells. Ability to release HRA, attach to antibody-basal cell-matrix complexes in vitro and to mediate cytopathic effects will be evaluated. These studies should provide insights into the nature and magnitude of the contribution of cellular and humoral components known to be associated with lesions of BP using a model which allows each to be evaluated and quantitated individually as well as in conjunction with the others as modulators.